Dark matter, Dark energy..

[psynapse]

AFAIK we don't know what it's composed of. I was wondering if the light that encircles a black hole could be immense enough to carry with it enough energy to be a significant form of mass.

Very bright intense light.

[timo]

Let´s say light circeling a black whole would contribute a significant amount of energy: How does that fit into the picture of either dark matter or dark energy? What would be the similar properties?

[psynapse]

I was thinking along the lines of there being so much energy in a confined space that it might have a tiny significant mass. I was wondering if this was possible with light as it is influenced by gravity (or travels a straight path in a warped space) if it could have it's own gravitational effects.

I realize this doesn't seem to make sense but I am talking a lot of light.

[timo]

I was thinking along the lines of there being so much energy in a confined space that it might have a tiny significant mass.

I´d spontaneously think so, yes. Let me just add that it might be better to think in the lines of "gravitational fields are created by energy" than in the lines of "grav. fields are created by mass" because mass can sometimes be a disambiguous term. (oh, and the "... created by energy" is not the whole picture, either - so don´t overstretch it).

 

I was wondering if this was possible with light as it is influenced by gravity (or travels a straight path in a warped space) if it could have it's own gravitational effects.

Electromagnetic waves (=light) and all other forms of energy contribute to the gravitational field.

 

To explain my 1st post: I was not arguing that photons around a black hole would not increase its mass (I could have done so, though). I was trying to clearify that your jump from "I found a source for gravity" to "so it could be dark matter or dark energy" is a bit (more than a bit) hasty. You´d neither get the distribution required for dark matter nor the exotic properties of dark energy with your ... well, it´s still just black holes with a bit more mass.

 

I realize this doesn't seem to make sense but I am talking a lot of light.

The amount doesn´t matter. The effect is either zero or not. If it´s zero, then it will also be zero for a lot of <stuff - light here>. If not, then it´s non-zero also for small amounts.

[ParanoiA]

I thought photons have zero mass. I thought that's why they could travel at c. So if light is electromagnetic waves that carry energy, then energy can travel at c...?

[timo]

In short: Yes.

[psynapse]

Does that only refer to a "rest mass"?

[Royston]

Does that only refer to a "rest mass"?

 

A photon 'is there' it just acts as though it has no mass, relative to anything else (besides gravity waves which also travel at the speed of light.) That's why it's speed is constant in any reference frame...and, as you said, why photons are regarded as having no 'rest' mass.

[ParanoiA]

A photon 'is there' it just acts as though it has no mass, relative to anything else (besides gravity waves which also travel at the speed of light.) That's why it's speed is constant in any reference frame...and, as you said, why photons are regarded as having no 'rest' mass.

 

If you have the patience and desire I would love to read an ellaboration on that. I don't know what you mean by "rest" mass. It sounds as if it might have something to do with energy being similar to mass on certain levels. And now that I'm reading about quantum uncertainty and quantum field theory, it's making me wonder if perhaps the energy keeps jumping around from photon to photon so that no single photon really "carries" the energy at c.

 

I don't know what the hell I'm talking about as I'm at that dangerous stage of learning where you know just enough to make an ass out of yourself if you're not careful.

[Gilded]

Rest mass is the mass of an object at rest (surprisingly). For most classical objects this is very close to the relativistic mass and perhaps that's the reason why people don't remember/know of it too often. And AFAIK something with no rest mass can't exist at rest (and is in fact forced to move at c?).

[swansont]

It's also useful because it is invariant under a transform to different inertial coordinate systems. i.e. all observers can agree on its value.

[Royston]

Yeah, pretty much what Gilded said, I was in the middle of a response and kept on getting distracted.

 

ParanoiA, it may be worth going back and reading up on Newtonian Mechanics, specifically the laws of motion, before worrying about quantum field theories et.c Once you have inertia sussed, then you can see what is meant by inertial frames, when you tackle relativity.

[Klaynos]

There is (imo) a pleasant formation of all the relativistic equations in which mass is ALWAYS kept as the rest mass...

[timo]

There is (imo) a pleasant formation of all the relativistic equations in which mass is ALWAYS kept as the rest mass...

I´m afraid I don´t understand what you are saying or trying to say.